The invention generally relates to a semiconductor device and a manufacturing method thereof. More particularly, the invention relates to a semiconductor device adapted to improve its production yield and a manufacturing method thereof.
As semiconductor devices become more highly integrated, the line width of the gate has been narrowed, and the gate channel length has decreased. However, this results in the generation of a defect whereby a transistor of the semiconductor device operates abnormally.
To solve this problem, a transistor which includes a recess gate is suggested. The recess gate allows a portion of the semiconductor substrate corresponding to a given gate region to be etched at a fixed depth, in order to increase the contact area between an active region and a gate. As such, the gate channel which lies between source/drain regions positioned on both sides of the gate is lengthened.
However, when the semiconductor substrate is partially etched in the formation of the recess gate, horns can remain because the bottom edges of the recess are not completely removed. Horns may result in the formation of a defective gate in the following process.
Also, a more highly integrated semiconductor device makes it more difficult to adjust the threshold voltage of a transistor by means of only the recess region. To this end, a bulb-type recess having an enlarged bottom portion which is formed in the transistor region is proposed. Although the bottom portion of the recess region is additionally etched in the formation of the bulb-type recess, horn-shaped residuals can remain. In accordance therewith, the defect can be generated and furthermore these residuals can cause a decrease in threshold voltage.
One of the most controversial matters is a short channel effect caused by the decrement of the gate channel length. Actually, the more highly integrated semiconductor devices require elements capable of operating at a higher-speed when at a lower operating voltage of about 1˜2 voltage. To this end, the threshold voltage of a transistor must be lowered. However, if the threshold voltage is lowered, it is difficult to control the operation of the transistor due to the short channel effect. Moreover, the short channel effect causes a DIBL (Drain Induced Built-in Leakage) phenomenon involving hot carriers.
To minimize the short channel effect, a variety of aspects regarding the semiconductor device have been researched, but the only way around this problem continues to be the high integration of the semiconductor device. For example, a method controlling the doping concentration has been used for the semiconductor device, but it cannot substantially prevent the short channel effect. Also, a method of forming an SSR (Super Steep Retrograde) channel and an ion implant channel through a vertically abrupt channel doping process has been used. An additional method of forming a halo-shaped channel through a laterally abrupt channel doping process and a large angle tilt implant process has been used.
The manufacturing method of the semiconductor device as described above is an attempt to form a channel length to be long enough to prevent the short channel effect, through the process of forming a gate on an active region and etching the active region to form a recess. However, several factors deteriorate the productivity of the semiconductor device. These factors include the reduced channel length due to the high integration of the semiconductor device, a moat caused by stripping a silicon nitride film during the formation of an isolation film, and a lowered threshold voltage due to the horns generated during the etching process when forming a recess gate.